Electro-mechanical sound reproduction devices have been employed since the early days of cylindrical wax recordings. Simply stated, a membrane of some sort is used in a piston action to mechanically move air, creating sound waves audible to the listener. The electro-mechanical “speaker” is the result of many years of engineering, in which a paper or plastic cone is affixed to a coil of wire. The coil is supplied with an iron core, and surrounded by a magnet. This arrangement surrounds the wire in a magnetic field, forming an electro-magnet. When an alternating current (AC) signal is applied to the coil, the coil moves with a piston action (back and forth). This moves the attached cone, pushing air, creating sound. This arrangement results in high quality sound reproduction, but is very heavy and requires a large amount of power to achieve audible sound levels.
A different form of sound producer is available known as a “piezoelectric element”. Piezoelectric elements are small, very lightweight, and require relatively low power to produce sound. The piezoelectric element includes a crystal that produces electricity when flexed, or flexes when an electrical current is applied. The crystal is mechanically bonded to a “carrier plate”, typically a small, thin brass disk. By applying an alternating current to the piezoelectric element, sound can be produced.
Because of the nature of the piezoelectric element, however, it is only capable of producing certain narrow band frequencies efficiently. Typically, piezoelectric elements are used for producing single tones at a “resonant frequency” (the frequency at which they require the lowest amount of power to produce the highest sound level). Different piezoelectric elements have different resonant frequencies.
However, conventional piezoelectric sound producing modules suffer from a number of drawbacks. They do not provide hi-fidelity sound, the volume is generally very low, and the sound quality is very poor. Devices that do produce hi-fidelity sound are generally too heavy for attaching to a balloon and require too much power to drive the device.
Accordingly, it would be advantageous to produce a sound module, which employs piezoelectric elements. It would further be advantageous to produce such a sound module that is designed to: be attached to a balloon, provide hi-fidelity sound, provide higher volume, reproduce prerecorded sound, and maintain sound quality even as the balloon begins to deflate.